Our previous studies have shown that many symptoms of and mortality from wasting disease induced with either cortisol acetate, endotoxin or by neonatal thymectomy were related to an infectious process or endotoxemia produced by the intestinal normal flora. This pathogenic mechanism appears to be preceded by immunosuppressive events which profoundly alter the anti-bacterial immune mechanism. Current studies include the wasting process that occurs naturally in the congenitally athymic mouse, nude, prematurely killing the animal. The nature and effect of the immunologic lesion in wasting diseases produced by endotoxin or cortisol acetate and the "natural" wasting process in the congenitally athymic mouse are the subject of continuing studies. In addition, the regulatory effect of gut immunity on the levels of intestinal normal flora will be examined in light of our recent observation that a depressed intestinal immunity (IgA) response contributes to an overgrowth of Escherichia coli and a marked susceptibility to their endotoxins in mice.